A website owner may find it useful to understand properties of visitors to the website. For example, the demographics of visitors to the website may be useful in selecting advertisements targeted to a particular portion of the website visitors. Some conventional systems use a panel-based approach in an attempt to acquire demographic information about website visitors. Individuals are invited to join a panel and software is installed on their computers, which monitors which websites they visit. The panelists are asked to provide demographic information. Accordingly, the information collected can be used to determine an estimated demographic for the visitors to certain websites. The panel-based approach might not provide useful information for infrequently visited websites. A survey-based approach has also been used. A survey can be placed on a given website soliciting visitors to provide their demographic information. However, it can be difficult to place surveys across a large number of websites, to ensure accurate visitor responses and to prevent spam attacks on surveys to bias answers. Further, response rates are generally low. Another approach can estimate demographics of website visitors using information known about persons living in a geographic location associated with an IP address of a visitor to the website.